Wet method of separating metallic compounds.



I The chief metals UNITED g- S JOHN HERBERT TI-IWAITES, OEPETERBOROUGH, NG A D.

WET METHOD OF SEPARATING METALLIG COMPOUNDS. I

No Drawing.

Specification of Letters Patent. Patented Sept. 28, h9g9; Application filed July 8, 1908. Serial No. 442,518.

To all whom it may concern:

Be it known that I, J OHN HERBERT Tum-urns, a subject of the King of Great Britain, residing at Market Chambers, Peterborough, in the county of Northampton, England, chemical engineer, have invented certain new and useful Improvements in Wet Methods of Separating Metallic Compounds, of which the following is a specification.

This'invention has for its object improven'ients in commercial methods of separating metallic compounds from solution-s contain-- ing one or more metals, whereby certain separations are carried out more quickly and more cleanly, or are carried out in a manner which gives precipitates that are more easily filtered off or otherwise separated from the liquid, than is the case with the methods usually employed; and also, if desired, compounds of only one metal, namely z-inc,'are used throughout for these separations, and this metal can be recovered in various ways and used over again.

Sulfureted hydrogen gas is often used to throw out of solution certain metals in the form of sulfids, which are-completely pr cipitated from acid solutions by this gas.

which behave in this manner are copper, lead, mercury, silver, arsenic, antimony, tin, bismuth, id cadmium. On a large scale the operation is by no means easy orsafe, as the gas is poisonous, and after a few inhalations its presence cannot for the time being be perceived by the sense of smell; the precipitation takes a long time for completion, and the precipitates produced arevcry bulky and difficult to deal with; the solution mustbe of acid reaction to prevent certain other metals from being irecipitat echand must be strongly acid under certain well-known conditions. If soluble sulfids are used instead of sulfureted hydrogen, an excess of acid must be maintained, and there is practically always an escape of sulfureted hydrogen which is both a loss and a nuisance, and a local excess of the soluble sulfid may cause the precipitation (if certain metals, such as cobalt and nickel, which is not desired, and which .cannot be remedied usually by a moderate excess of acid, for once the sulfids of these two metals are precipitated, dilute acids will not re-disst-ilve them generally. I

Seraph-on is in some cases used instead of sulfureted hydrogen, to remove certain of the metals named above, such as copper, but some metals such as cadmium are not precipitated by metallic iron. This method introduces iron salts into the solution remaining, and the precipitate obtained is also contaminated with iron. Metallic zinc is also sometimes used, but in the case of both metallic iron andnaetallic zinc a large amount of tank or other space is necessary, and a considerable time is required to remove the last traces of the precipitable metals. Instead of using any of these means by this in-Ivention I take advantage of the fact which I have discovered, that zinc sulfid, a known precipitant for certain of the heavy metals, may be applied to precipitate from a liquor containing a number of heavy metals, compounds of these metals in several suc cessive groups by causing the zinc sulfid-to act on :the liquor under successively varied conditions.

I use zinc sulfi-d preferably recently precipitated. Itis added to the substantially neutral solution as a fine powder or as a cream or milk, or otherwise as may be found most convenient, and it is economical, both of time and of zinc siilfid, to use an apparatus which provides agitation and which has an arrangement by means of which the formation of small cores of the precipitant is prevented or cured. Such an apparatus is simple, and it can be constructed for continuous instead of intermittent work if desired. The following metals, or such of them as may be present, are completely thrown down as sulfids in the cold orhot: silver, lead, mercury, copper, bismuth and tin, and when present in their capacitim of bases or lower oxygen acids, arsenic and antimony as we'll; whereas cadmium is not thrown down unless the temperature is raised to near the boiling point, so that a handy means of separating this metal from :the others just mentioned is alforded, which is not the case if su'lfureted hydrogen is used. Arsenic and antimony present as arsenates and antimonates areonly precipitated by zinc sulfid from solutions which are decidedly acid.

To precipitate arsenic and antimony from- .arsenates and aintimonates, the solution must be decidedly acid; in which case zinc sulfid behaves just as sulfuretcd hydrogen, throwing down the same metals. includiug cadmium in the cold as Well as in the hot but. i there are these differences there need be practically no evolution or sulfureted hydrogen gas, the precipitation is practically nstantaneous, even with arscnates, and the precipitates are less bulky.v

- The following equations are typical of;

. sulfid is added to the liquor to determine .the precipitant which has been .used'can be -.or the precipitate may be added to the next batch of'liq'uor in order to use up its'con- .tained excess of zinc sulfid.

-made so as to render possible a calculation :in order to ascertain whatquantity of zinc sulfid is tobe. added to the bulk to avoid condition being that the reagent is thoroughly mixed with the liquors in question,

nickel, cobalt, iron and chromium, from all :one; cadmium in another; and arsenic and- .At .the same time, the second group contain ing cadmium, can be obtained if. desired :in; the same precipitate as either the first o'rgthe'. third group, under the conditions set'ifoiith the reactions which take place 1-- i .-sb,s +sznoi +euaoi+inui WV hen any metal is precipitated by means dissolves the solution, and any excess of dissolved out of the precipitate by treating it with very dilute acid in most cases this can be. done before .the vprecipitate is .filtered ofi', or otherwise removed from the liquid :It will be understood that suflicient zinc the precipitation of the sulfid as aforesaid, and unless an analysis 01 the liquor has been ofthe amount of zinc sultid required accord.- mg to princ ples well known to chemists, a trial should be conducted on a small port-ion using anunnecessary excess. All the reactlons 0t zinc sulfid herein described are. practically instantaneous, the one essential lumps-being avoided.

By the use of zinc sulfid a very convenient means is thus provided for completely separating all the above-named metalsexcept the other coimnonly-occurring metals, and'i'n such a manner that they may themselves .be divided into three groups, namely silver, lead, mercury, copper, bismuth and tin in above. v

The metals are precipitated as sultids, and

5 copper the quantity of zinc sulfid necessary to pre- 5 cipitate them is easily calculated from the well known chemical equivalents, I

'ilhe tollowing would be a treatment under this invention of '1 cubic meter of a substantially neutral liquor obtainedfrom zinciterous pyrites cinder by roasting with connnon salt. und-containing per liter grams oi 2H grains ofcadmimmand grams Na HAsQQ.

01" arsenic as sodium arsenate The equation illustrating the precipitation oi the arsenic is as follows:

The quantities of zinc sulfid necessary to precipitate the copper, cadmium and arsenic, are 32.5) .kgs., 2.44 kgs., and 8.12 kgs, respectively.

added to the cubic meter of liquor, and the resulting precipitate, containing 21.2 kgs. of copper, is filtered off. 2. l4kgs. more of zinc-sulfid .is added to the filtrate which is heated nearly to boiling (say 0.) either before or after the addition, the only condition being that the liquor is at such temperature while the zinc sulfid is present; the re sult-ing precipitate, containing 2.8 kgs. of

32.5 kilos of zinc sulfid are I cadmium as sultid, is filtered ofii. To the filtrateis then added 8.12 kgs. more of zinc sulfid and either sulfuric or hydrochloric acid equivalent to at least 8.5 kgs. of pure H01, when the 2.5 kgs. of arsenic is precipitated as sulfid. i

The following would be a treatment under this invention of 1 cubic meter of a substantially neutral liquor containing per liter 10.8 grams of silver, 1.03 grams of lead, and 2.5 grams of arsenic. The quantities ofizinc sulfid necessary to precipitate these metals out of the cubic meter are 4.87, 0. 19 and 8.12 kgs., respectively.

5.36 kilos'ofzinc sulfid is added to the 3 liquor, and the resulting precipitate, containing 10.8 kilos of silver and 1.03 kilos of lead, as sulfids, is filteredoft'. The 2.5 kgs. of arsenic left in the filtrate is precipitated out by the addition of 8.12 kgS. 11'10r of zinc sullid together with sulfuric or hydrochloric acid equivalent to atdeast 8.12 kgs. of pure H01.

Having thus :described the nature oflmy saidinvention and the best means I know of carrying-tile claim 1. "A process for separating sulfide of silver, lead, mercury, copper,-bis1nutl1, tin, cadmium, arsenic and antimony into three groups, .one group containing silver, lead, mercury, copper, bismuth and tin, the second'cgro'up containing cadmium, and the ithjzl'd group containing arsenic and antitreating ;a substantially neutral liquor con- :same into practical effect, I

more zinc sulfid, removing the precipitate taining the compounds with zinc sulfid, removing from the liquor the precipitate formed, and treating the liquor withacid and zinc sulfid.

2. A process for separating into groups sulfids of silver, lead, mercury, copper, bismuth, tin, cadmium, arsenic and'antimony, which process consists in treating a cold, substantially neutral liquor containing the compounds with zinc sulfid, removing from the liquor the precipitate formed, heating the liquor, treating the heated liquor with from the liquor, and treating the liquor With acid and zinc sulfid.

l l 3. A process for separating into groups! sulfids of silver, lead, mercury, copper, bismuth, tin,.cadmium, arsenic and antimony, which process consists in treating a cold, substantially neutral liquor containing the compounds with zinc sulfid, removing from the liquor the precipitate formed, heating the liquor and treating the heated liquor with more zinc sulfid.

' In testimony whereof I have signed my name to this specification in th presence of two subscribing Witnesses.

JOHN HERBERT THVVAITES 7 W. J. SKERTEN. 

